Fortunately, the answer’s easy – but it requires a Google Webmaster Tools account.
Log into your Google Webmaster Tools account and navigate to:
Site Configuration >> Crawler Access >> Remove URL
Now click the grey ‘new removal request’ button, and enter the exact URL of the page you want to remove from Google’s index, then click ‘continue’.
Now you will have a drop-down with 3 options:
- Remove page from search results and cache
- Remove page from cache only
- Remove directory
In the majority of cases, you’ll want the first option (‘remove page from search results and cache’), so select this and click ‘Submit Request’.
Normally it will take Google a couple of days to flush out all instances of the page from it’s index, but essentially – that’s it.