The Trademark Clearinghouse is one large worldwide database that contains the information relative to all trademarks and rights holders. It was conceived as a tool for protection against third parties who register a domain name in the new gTLDs that coincides with a registered trademark.
Registration in the Trademark Clearinghouse is obligatory if you wish to register your mark in the new gTLDs during what this knows as the Sunrise Phase (the initial period aimed at the rights holders before registration becomes free). With one sole validation of your trademark you will be able to access all the Sunrise Services without paying additional fees.
The rights holder of the trademark will receive a notification when an outside third party registers a domain that coincides with his.