Greetings in that Divine and Most Precious Name of Our Lord and Savior Jesus Christ!
I understand that you have to be baptized an Orthodox Christian to receive communion in an Orthodox church but can an Eritrean Orthodox Christian take communion in a Greek Orthodox Church and vise verse? Because I'm Eritrean Orthodox and I attend a Greek Orthodox Church and all of the other Eritreans there take communion there.
While I am entirely for the unity of the Churches, and the continual ecumenical dialogue in that direction, and at every instance of praying of the One, Holy, Catholic, Apostolic Church I also pray deep in my heart and soul for the true unification of our Churches, I must confess that I understand the Greek Church not to be in communion with the Eritrean Orthodox Tewahedo Church at this time.
The Greek Church is Chalcedonian, they do not necessarily teach their Christology in the same light that the Tewahedo theologians of Egypt, Ethiopia and Eritrea have always taught over the past 1500 years. I would advice you sincerely to consult an Eritrean Tewahedo priest about this matter, even if just by email, as it would seem that you may not have one local or I would assume you would just commune in a Eritrean church
Are there no Syrian Orthodox or Coptic Egyptian (or, gasp, Ethiopian) churches in your area, the Tewahedo churches of Ethiopia and Eritrea are in full communion with Alexandrian Coptic Churches. This is not to disrespect any of our Chalcedonian brothers and sisters, but I am sure that even if you spoke with the Greek clergy there, they would be sympathetic and express similar concerns.
Though even in matters of sister churches in full communion, it is wise to consult the clergy beforehand to let them know you are planning to commune with their parish and that you have received proper Reconciliation in due respect to Tradition.