Widebody Captain reported suspected GPS jamming or interference in the vicinity of the Black Sea.

Narrative

While cruising at FL360 an amber ADS-B OUT EICAS alert displayed while we were approximately over GOKPA. About 20 minutes later an amber TERR POS EICAS alert displayed. The alerts extinguished about 50 minutes later at approximately 90 NM north of REVDA. Before departing ZZZ for DEL; as a crew during our preflight briefing; we discussed this threat as possibly occurring while flying in the vicinity of the Black Sea. I do not recall the source of our information; whether it was other crew previous experience on flights to and from DEL or other source. But the preflight discussion centered around the possibility of GPS interference in the area of the Black Sea and that if it should occur; we would experience the ADS-B OUT and TERR POS EICAS messages. We also briefly discussed that the EICAS messages would only be displayed while in the vicinity of the Black Sea. I have flown 5 or 6 DEL flights from ZZZ in the past 6 months; the last being two weeks ago. This flight was the first time I experienced this apparently expected GPS interference. Further discussion with the crew indicated to me that this interference is becoming more frequent lately.