DNS Flush
Windows (2000, XP, and Server other than NT4.0)
ipconfig/flushdns
Linux
the nscd daemon manages the DNS cache.
To flush the DNS cache, restart the nscd daemon.
To restart the nscd daemon, use the command `/etc/rc.d/init.d/nscd restart`
MAC
lookupd -flushcache
REF:http://www.tech-faq.com/flush-dns.shtml