You can automate this process too. Using the console installed on your Core Server, go to Configure - Services, and on the Inventory tab you can set the number of days to keep scans before deletion. If the inventory record hasn't been updated in that amount of time, the system will automatically delete it. Also check out the duplicate deletion; since you have systems that are being rebuilt, if they retain the same MAC address and/or machine name, the old record can automatically be deleted too.
Mark Star - MarXtar LANDesk Enhancements
Home of Power State Notifier & Wake-On-WAN for LANDesk