Note: Clients that have been imported from Active Directory cannot be deleted using the below steps. Clients imported from Active Directory to the SEPM need to be deleted from Active Directory and then synced with SEPM in order for the clients to be removed. It will take approximately 45 days for the decommissioned clients to drop out all of the reports.

1. Open the SEPM and click on Admin in the left pane.
2. In the middle panel click Domains, and then click Edit Domain Properties
3. Within the General tab, you should see the option "Delete clients that have not connected for specified time."