CiviCRM Community Forums (archive)

Hi - a client had an external forum imported to Drupal. Drupal Users were created for all those forum users. No matching was done in this process.
So we are now looking at several hundred duplicates where, in most cases, original CiviCRM contact has no Drupal User, new CiviCRM contact has Drupal User, and an email address, and nothing else.

I was hoping I could do something along the lines of
- find all CiviCRM contacts created from the Forum import and DELETE, and thereby 'orphan' the Drupal Users
- run the Synchronize Users to Contacts whereby it will match the orphaned Drupal users to the civicrm record with the matching email

My testing shows this failed and instead I have a Drupal User that still thinks it has a Contact Dashboard.

Is there something else that needs clearing out of the UF Match table or some other table, to help fully orphan the Drupal User before I can successfully run the Synchronize Users to Contacts?