Below is how to clear / flush the DNS cache in Mac OSX.
(1) Open the terminal (Finder -> Applications -> Utilities -> Terminal)
(2a) In case your operating system is ‘Leopard’ (10.5.*) or ‘Snow Leopard’ (10.6.*), issue the following command:
(2b) Otherwise, for older operating systems, issue the following command:
This is the equivalent of the following Windows command: ipconfig /flushdns