Green’s Dictionary of Slang

(UK Und.) a knockout blow.

1865		Leaves from Diary of Celebrated Burglar 100/1: Nothing would be easier than for us to lay for him and give him a ‘domino’ with a ‘neddy’ and ‘collar’ the note case he carried and its contents.
1866		Wild Boys of London I 55/2: He received what the Dolphin called a ‘domino’ on the crust, and he went up blinking like an owl.
1873		Illus. Police News 9 Aug. 4/3: [O]ne of them said that they intended give him a ‘domino’ (a slang term used by thieves, meaning to knock a man down and rob him), and they asked him to ‘Philip’ for them (that is, look out for the police while the robbery was being committed).
1898		J.D. Brayshaw Slum Silhouettes 3: ’E could ’andle ’is dooks, an’ no error: the way ’e set abaht Bill was a fair treat [...] popped in fust ’is left an’ then ’is right, droppin’ Bill a domino every time.
1945		(con. late 18C–mid-19C) Baker Aus. Lang. 44: Domino, the last lash in a flogging.
1973		(ref. to 1890s) ‘Gloss. of Larrikin Terms’ in J. Murray Larrikins 202: domino: the final lash of a flogging.
1980		Barltrop & Wolveridge Muvver Tongue 69: ‘I didn’t half pay him’ [...] is another way of saying that he received a domino, or a right doughboy.