When you right-click a DNS server in the DNS snap-in, and press Scavenge Stale Resource Records, your DNS Server event log records:

Event Type: Information
Event Source: DNS
Event ID: 2502
Event Category: None
Description: The DNS server has completed a scavenging cycle but no nodes were visited. Possible causes of this condition include:

1) No zones are configured for scavenging by this server.
2) A scavenging cycle was performed within the last 60 minutes.
3) An error occurred during scavenging.

The next scavenging cycle is scheduled to run in 0 hours.

The event data will contain the error code if there was an error during the scavenging cycle.

For more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp.

If you manually scavenge a DNS zone that supports dynamic updates, prior to the Date and time: in the The zone can be scavenged after box on the General tab of  the zones' Properties, you will receive the above event.

NOTE: If The zone can be scavenged after box is missing from the General tab, select Advanced on the View menu of the DNS snap-in.

For additional information about scavenging and aging DNS resource records, see http://www.microsoft.com/resources/documentation/WindowsServ/2003/standard/proddocs/en-us/sag_DNS_imp_ManageAgingScavenging.asp.