Yep, I went in to make sure terms were correct, (and they were) and checking out my disk usage now as well. it doesn't break it down by domain, but by user, so it is useful to that level.
It depends on when you deleted, the usage goes on a 30 day average so until they have been gone 30 days it won't be '100%' gone from the accounting of disk space, each day it snapshots the used space, it calculated this in the 'average' and then of course each day that passes after the delete it will have less bearing on the used space.