Green’s Dictionary of Slang

(Aus./N.Z.) to hit someone on the head.

1953		T.A.G. Hungerford Riverslake 26: He’ll scone that galah [...] Look out, Jerry – he’ll do the knob any minute!
1988		McGill Dict. of Kiwi Sl. 97/1: scone head, or hit somebody on the head, usually its top.
2003		McGill Reed Dict. of N.Z. Sl.