To flush DNS cache in Microsoft Windows :
C:>ipconfig /flushdns
To flush the DNS cache in Linux:
# /etc/rc.d/init.d/nscd restart
To flush the DNS cache in Mac OS X Leopard:
$ lookupd -flushcache
To flush the DNS cache in Mac OS X:
$ dscacheutil -flushcache
Certainly rebooting your computer always works.