Green’s Dictionary of Slang

(Irish) as an intensifier, absolutely, utterly.

1863		E. Gaskell Sylvia’s Lovers II 122: He were sore put about because Hester had gi’en him the bucket.
1943		(con. 1850s) G.A. Little Malachi Horan Remembers 24: But poor Frank Lynam was sore upset.