Domestic animals backing part of procedure (4)
I believe the answer is:
step
'procedure' is the definition.
(I've seen this in another clue)
'domestic animals backing' is the wordplay.
'domestic animals' becomes 'pets' (animals in the home).
'backing' is a reversal indicator.
'pets' written backwards gives 'STEP'.
'part of' is the link.
(Other definitions for step that I've seen before include "Bit of mashed potato maybe" , "Pest (anag.)" , "Foot movement" , "Tread - stage" , "Footprint" .)