What is DNS Caching
When you visit a web site, your connection goes from your browser to your ISP, and from there through switches and finally to where the site is hosted. These servers and switches your connection goes through along the way save in cache memory where the services for your domain are.
These servers will keep this saved information for a fixed period of time which can range from five minutes to potentially up to a week. The period of time DNS is cached should come from the TTL value given in the zone file for the domain.
How DNS Caching can affect your updates
When you make a change in DNS for your domain, DNS caching can prevent your ability from seeing the update happen. DNS caching usually affects recent visitors to your site, but not most viewers.
What you can do if you're experiencing DNS caching
You can try contacting your ISP to have them refresh their cached value. In our experience, most ISPs however will not do this for you.
The bad news is that there really isn't anything you can do in cases like this but wait. DNS caching is a practice that works very well most of the time, and helps improve performance on the Internet. The vast majority of your site's visitors will likely not be affected by this.
Local DNS caching
In some case, the caching happens locally on your computer. To clear local cache, do the following:
On a Windows computer, go to Start->Run, and type in ipconfig /flushdns
For a Mac or Linux computer, go to the console/shell, type in dscacheutil -flushcache and hit enter.