Green’s Dictionary of Slang

(Aus./US) extreme, complete.

1862		T. Winthrop John Brent 279: That are’s wut I call a screechin’ good price fur an old one-eyed nigger.
1902		Bulletin (Sydney) 22 Nov. 16/2: The idea of praying for rain, too, is a screeching absurdity.
1907		Dly Arizona Silver Belt (Globe, AZ) 15 Mar. 6/2: Screeching comedy ‘Rescued in Mid Air,’ at the Iris tonight.
2012		Independent 24 Jan. 36/1: To me it’s so screechingly obvious.