Google last month launched a Chrome extension with the exact same functionality, but the search giant has now made it an official feature. Whenever you head back to Google after checking out a search result, it will display an option to block all results from that domain.
Once a website is blocked, you can either manage your blocked sites or undo the block. You have to be logged in to your Google account in order to save a blocked website. Search results with blocked results will display a message saying how many results were blocked.
Google said in its announcement Thursday that it's adding this feature to provide a more personalized Google experience, but if Google's Personal Blocklist extension is any indication, the company is also trying to clean up spam within search. By having users pick out low-quality websites, Google can quickly pinpoint spam and content farms.
Google says it is not "currently using the domains people block as a signal in [search] ranking," but that it may utilize it in the future. Don't be surprised if blocked search results become a key component of searching in the future.