Green’s Dictionary of Slang

(US) in no way at all.

1954		(con. 1920s–30s) J.O. Killens Youngblood (1956) 59: White folks got everything. Niggers ain’t from doodly-squat.
1961		M. Terry Old Liberty (1962) 7: He just couldn’t see doodle-squat out of one eye.
2002		(con. 1998–2000) J. Lerner You Got Nothing Coming 52: A sharpened toothbrush would have availed me doodley-squat against this black giant.