The 7-Series GT transceivers require a GTRXRESET when RX Serial Data is lost.
The RX Serial data will be lost when a cable is unplugged or the link partner is reset.
The GTRXRESET is needed to be able to recover block lock in the core.
The 10-Gigabit Ethernet PCS/PMA v4.1 (Rev. 1) in 2014.1 adds a watch dog timer to check if block lock stays low and if it does issues a GTRXRESET.
Current and previous versions of the core also monitored for idle data of alternating 0's and 1's on RX data out of the GT and have a watch dog timer to issue a GTRXRESET if this is found.