Green’s Dictionary of Slang

an excl. of denial, disdain: ‘get away!’ ‘get out of here!’.

1867		Chicago Republican 24 July 8/1: [Baseball] players invariably say ‘Shoo-fly’, when they make a miss.
1889		Farmer Americanisms 484/2: Shoo! fly! don’t bother me! An exclamation of impatience. Shoo and fly are both common ejaculations in country districts when driving wandering fowls or cattle from gardens etc., to legitimate pastures... The full phrase is now familiarly colloquial.
1893		‘’Arriet on Labour’ in Punch 26 Aug. 88/1: ‘Labour!’ I sez, ‘Oh, shoo fly, Sam! You ’orny-’anded codgers— / [...] / are reglar Artful Dodgers.’.
1896		Meridional (Abbeville, LA) 7 Mar. 2/1: Sambo move / With swift acceleration; / For I’m a Pharr [...] of Sugar-teat persuasion, / Shoo-fly coon.
1919		Mencken Amer. Lang. 311: Shoo-fly afflicted the American people for at least two years, and ‘I don’t think’ and aber nit quite as long.
2013		T. Robinson Hard Bounce [ebook] The landlord cut me a deal when 4DC shoo-flyed some meth-head squatters from another one of his properties.