hi,

You can configure automatica delete setting

 Configure SEPM to remove clients which have not connected within a specific number of days.

1. Open SEPM and select the Admin panel.
2. Click on Servers
3. Right click on the Site where your management servers are located and choose Edit Properties
4. Check "Delete Clients that have not connected for __ Days"
5. Enter a value for Days.
6. Click OK.

NOTE: In version 12.1 of the SEPM, the location for adjusting the setting to delete clients which have not connected for X number of days has moved:

1. In the SEPM, go to the Admin page.
2. Select Domains.
3. Under Tasks, select Edit Domain Properties.
4. In the Edit Domain Properties window, on the default General tab, note the option to "Delete clients that have not connected for specified time."

Configuring a low value for this setting would clear up the duplicates more quickly