On this page: admin.php?users/search, we have the option to select from a list of the various secondary user groups. So, if you check off "group A" and click search, you will get a list of users in group A. If you select group A -AND- group B, the results will be a list of all users that belong to either of those groups.
It would be helpful to be able to optionally modify these search results to only include users that are in both group A and group B.
A solution might be a "require all user groups" checkbox.