Use the below syntax from the Terminal window on a Macintosh computer running OS X 10.5 (Leopard) to clear the DNS cache for the computer.
dscacheutil -flushcache
You might need to flush the DNS cache if you know a DNS change has been made recently but your Mac is not showing the change. OS X does a good job of DNS caching but it may take longer than you want to wait to update a changed DNS setting and running the above command will solve your issue without having to reboot.
