Cache Information

The exchange server recently changed IP address, Most all NT machines seem to ping the netbios name fine. I have 2 machines when you type ping SFEXCH2, the old IP address comes up and then Request Timed Out. Is this cached information on the machinethat can be purged or more to do with WINS. I’ve tried the NBTSTAT command and also deleted the LMhosts file. DHCP does hand out everything to the machine.