How can I can archive contacts that exist in only one group? I want to decommission a group and archive only those contacts that have membership in only that one group. I don't want to archive the contacts that have memberships in other groups.
There is not a function within groups to only identify contacts that don't belong to any other groups, you can, however, create a segment that does this!
Head to audience > segments > create a new segment to get started. From here you can find contacts based on group membership and add parameters for *in* and *not in* groups to find exactly what you are looking for.
The other alternative would be to create a segment based on some other criteria, such as data in a contact field. You can utilize 'fields' as an option to narrow these down.
After you've created the segment, head back into the segment itself choose actions > archive all to remove the contacts from within it.
Feel free to have a look on our article for segment building here: