Google recently released a new way to implement and manage 404 error pages. 

Below is a screenshot of the widget.

404 error pages are those pages that are displayed when you try to access a page that no longer exists on a website. Marketers often try to optimize these pages to ensure that if a visitor lands on one of these pages they do not leave the site altogether. Another common trick is to try to cross promote products and services via 404 error pages.

This domain has been several things over the last few years so I have a number of pages indexed in google that are no longer active. So I am trying out this widget on my site in hopes that it may communicate with Google technology and help remove outdated indexes sooner. (I have no proof of this, just hoping)

You can se the widget in action here: http://www.mckyton.com/doesnotexist

I am using the default widget setting but you can customize the look to your liking.