To clear the DNS cache on your computer, you need to flush the DNS caching. Instructions to flush the DNS, in accordance with your operating system, are given below :

To flush the DNS cache in Microsoft Windows (Win XP, Win ME, Win 2000):

Start -> Run -> type cmd

In command prompt, type:  ipconfig /flushdns

To flush the DNS cache in Linux, restart the nscd daemon:

Type /etc/rc.d/init.d/nscd restart in your terminal.

To flush the DNS resolver cache in Mac OSX Leopard

you can use the command dscacheutil -flushcache :
bash-2.05a$ dscacheutil -flushcache

To flush the DNS resolver cache in Mac OSX versions 10.5.1 and before

the command lookupd -flushcache will perform the same task:
bash-2.05a$ lookupd -flushcache