It's buried in the ICAO GOLD.
"With the FANS-1/A application, an ATSP receiving a CPDLC transfer does not have confirmation they are current date authority (CDA) until a downlink is received from the aircraft. The ATSPs are unable to reach global agreement on whether this confirmation is needed, and those that require confirmation are unable to reach agreement on a common procedure to achieve this."
As of June 2010, Anchorage, Auckland, Brisbane, Fukuoka, Jo-burg, Mauritius, Melbourne, Nadi, Oakland, Singapore and Tahiti wanted a report crossing the boundry. New York specifically says not to send a
PR. Shanwick and Gander only want a message if your next ETA changes 3 minutes or more and Reyk and Santa Maria will confirm CPDLC change over with an uplink message you "roger."