purging entries for schemas no longer installed?

Is there a way to automatically purge schema entries for entries that 
are no longer installed in the system?

Namely, lets say I install evolution.  If I want to remove it in debian, 
I could a dpkg --purge evolution.

this will remove the schemas, but whatever changes I made to my local 
gconf will still exist.  What happens if I made some bad configuration 
choices that I really want to revert, but dont know whats breaking it? 
I can't seem to find a way to either

a) take a schema and revert all key values to their default

or preferably for this case

b) see what schamas are installed and remove any keys that don't have 
their schemas installed anymore.

The closest thing to "b" I can see is that I can probe each key and see 
if it has a schema (if I remove the schemas it seems to come up "no 
schema known" and then "unset" them.  But I think this would just result 
in a situation where one has empty values if it would be reinstalled, 
not default values (though I could be wrong I guess).

any help would be appreciated.

thanks.