The page files on your comp.
A rummage through the avastUI will give you a better understanding of avast, File System Shield, Exclusions, see image.
However, I don't know if the on-demand scans would scan it as there is no defined exclusion in the avast Settings, Exclusions, which apply to all on-demand scans.
So they aren't scanned whilst in use swapping in and out memory objects.