The easiest possibility right now is probably to search in an indexed group for imported items ( item!:indexed) or in an imported group for indexed items (item:indexed). Depending on the number of groups to search in this might become cumbersome unfortunately.
But maybe this would be a good addition for the Info filter.
I wrote a script that creates smart groups for all selected groups. It can be used from inside smart groups so it should be easy to create everything in one go.