Rub hard (5)
'rub hard' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for scrub that I've seen before include "Cancel (informal)" , "Rub hard to clean" , "Stunted growth" , "Get rid of" , "Cleanse" .)
(Other definitions for scour that I've seen before include "Full" , "search in detail" , "Thoroughly clean" , "Scrub clean" , "Clean by abrasion" .)