How you clear the DNS cache on OS X has changed yet again…
DNS caching is a good thing in general, it speeds up your browsing by not having to request the same information over and over. However, if you are making changes to DNS, they will not appear until the cache expires.
On 10.10 Yosemite clearing the DNS cache is now done by running:
For the record:
(OS X > 10.6 && OS X < 10.10):
OS X <= 10.6: