The local DNS cache in your machine will store the locations  of web-servers/websites that contain pages which you have recently viewed.

If the location of these pages have  changed, you will be unable to access them due to the local DNS cache ( the one cached by your local machine, which you use to access the webpages )

Following shows you on how to clear DNS cache on different platforms :

* On a system running in windows, navigate to cmd and run the following :

# ipconfig/flushdns

* On a system running on OS X Mountain Lion, type in the following from terminal :

# sudo killall -HUP mDNSResponder

* On a system running on linux distro’s, run the following :

# sudo /etc/init.d/nscd restart

Install nscd ( name service cache daemon ) if not present :

# sudo apt-get install nscd or yum install nscd