1. The Time To Live (TTL) has expired.
2. DNS has been shutdown.
3. The MaxCacheTtl value on the DNS server has expired.
To prevent DNS from caching records from recursive queries, use Regedt32 to navigate to:
On the Edit menu, Add Value name MaxCacheTtl, as a type REG_DWORD. In the DWORD Editor, set the data value to 0.
You must shutdown and restart the DNS server.