DNS stands for Domain Name System. This System translates a domain name such as thepicky.com into the not-so-friendly IP numbers like 18.104.22.168, to find the correct web site as well as for other information.
When you visit a website for the first time, it stores the information in cache for faster access.
If a there is DNS change in the internet, it might not reflected to your computer as it is cached already, if that is the case either you have to wait maximum of 24 hours for it to be dropped from the cache automatically or flush the DNS cache manually.
Here is how to Flush DNS Cache
To flush the DNS cache in windows, open the command prompt and type : ipconfig /flushdns
Start ==> Run ==> type cmd ==> type ipconfig /flushdns
To flush the DNS cache in Linux use the following command using a shell prompt
sudo /etc/init.d/nscd restart