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