Your network contains an Active Directory domain named contoso.com. Contoso.com
contains two domain controllers named DC1 and DC2. DC1 and DC2 are configured as DNS
servers and host the Active Directoryintegrated zone for contoso.com.
From DNS Manager on DC1, you enable scavenging for the contoso.com zone.
You discover stale DNS records in the zone.
You need to ensure that the stale DNS records are deleted from contoso.com.
What should you do?

A.
From DNS Manager, enable scavenging on DC1.

B.
From DNS Manager, reload the zone.

C.
Run dnscmd.exe and specify the ageallrecords parameter.

D.
Run dnscmd.exe and specify the startscavenging parameter.

Explanation:
According to Technet the answer should be A (“From DNS Manager, enable scavenging on
DC1″). Scavenging has been enabled for the zone, but it also needs te be enabled on the
server.

http://technet.microsoft.com/en-us/library/cc771677.aspx
Prerequisites for aging and scavenging
Before you can use the aging and scavenging features of DNS, several conditions must be
met:
Scavenging and aging must be enabled, both at the DNS server and on the zone.