Green’s Dictionary of Slang

1. (Aus./N.Z.) a rough, unkempt person; by ext. an outsider.

1852		Bell’s Life in Sydney 2 Oct. 1/3: ‘Not so fast,’ said Forky [...] ‘this Jacob was invented for gentlemen like me, not for scrubbers like you’.
1865		H. Kingsley Hillyars and Burtons (1870) 329: The auctioneer began: ‘Silence, gentlemen, pray silence.’ ‘Silence yourself, you old scrubber,’ was the polite rejoinder.
1898		E.E. Morris Austral Eng. 408/2: Scrubber (3) The word is sometimes applied to mankind in the slang sense of an ‘outsider.’.
1904		Sun. Times (Perth) 14 Aug. 4/8: The Groper-born Weld Clubbers / Will mingle with the scrubbers / The hoi polloi and pubbers.
1912		Bulletin (Sydney) 11 July 13/2: Once saw some ‘scrubbers’ – newchums of the runaway sailor class, imitate the practised bushman.

2. (also scrubbie) a cow or horse that has run wild in the scrub and has deteriorated in condition.

1857		Bell’s Life in Victoria (Melbourne) 4 Apr. 4/1: ‘But the cattle, by jingo [...] were the wildest brutes the eyes of man ever looked upon [...] the d—d’st scrubbers that over rushed a fence’.
1859		H. Kingsley Recollections of G. Hamlyn (1891) 212: ‘Scrubbers, eh?’ said the Major; ‘well, we must take what we can catch.’.
1865		Sydney Morn. Herald 26 Oct. 2/2/5: [T]he prisoner [...] said he and Jim ran it [i.e. a horse] in off the sand hills, and she was got bv a scrubber.
1874		W.H.L. Ranken Dominion of Aus. 110: There are few field-sports anywhere equal to ‘hunting scrubbers.’.
1888		‘Rolf Boldrewood’ Robbery Under Arms (1922) 71: Don’t be tearing away through thick timber like a mallee scrubber that’s got into the open and sees the devil behind him.
1899		‘Tom Bluegum’ Backblocks’ Parson 71: Scrubbers were stray lots of cattle which, having forsaken the open pasture-lands, found a habitat in the [...] scrubs.
1905		‘Mustering Song’ in ‘Banjo’ Paterson Old Bush Songs 113: We’ve got ’em now—the cows and calves [...] Strangers, workers, and milkers, too, / Of scrubbers also not a few.
1931		‘William Hatfield’ Sheepmates 245: They’ll [...] get a gutful o’ gallopin’ an’ start booin’ around lookin’ for the fool scrubber that started ’em orf to give him a well-earned poke in the bingie.
1946		A. Marshall ‘Grey Kangaroo’ in Tell Us About the Turkey, Jo 17: They were almost black—‘scrubbers,’ the old man called them.
1950		(con. 1936–46) K.S. Prichard Winged Seeds (1984) 168: Not a move out of those blasted scrubbers.
1967		‘Whisper All Aussie Dict.’ in Kings Cross Whisper (Sydney) xxxix 4/4: scrubber: Wild untamed cattle.
1975		R. Macklin Queenslander 110: An old scrubber bull reared to his feet.
1986		R. Beckett Dinkum Aussie Dict. 45: Scrubber: A cow or steer that has gone wild in the scrub.
1996		J. Byrell Lairs, Urgers & Coat-Tuggers 257: ‘They’re gonna give this promising three-year-old from up Newcastle way a bit of a workout against the scrubbies’.

3. an unpleasant weakling.

1895		C. Crowe Aus. Sl. Dict. 71: Scrubber, a worthless man.
1900–10		Stephens & O’Brien Materials for a Dict. of Aus. Sl. [unpub. ms.] 134: SCRUBBER: slang a cad, a nobody, a person of mean, dispicable [sic] or ill-favoured parts.
1904		Truth (Sydney) 10 July 1/2: The Foreign Jew and / Dirty Scrubbers. Forgers, Thieves, / Coolie half-breeds— Damned Peruvians.
1941		Baker Popular Dict. Aus. Sl. 64: Scrubbers, [...] (2) Any weedy or unpleasant person.
1963		A. Baron Lowlife (2001) 174: Some scrubber, some no-good dog that doesn’t stand a chance, some cripple, takes a fancy to nose him.
1968		G. Slatter Pagan Game (1969) 163: Hungry-gutted bastards — What a bunch of scrubbers.

4. in derog. terms for a woman [? SE scrubber, a charwoman, one who scrubs; sexual aspects suggest poss. link to Aus. term, defined as ‘a mare that runs wild in the scrub country, copulating indiscriminately with stray stallions’ (OED)].