In the fine CDF documents Communionis notio and Dominus Iesus, the Church's Magisterium clarified the position of those Christian bodies which possess true ministry and Sacraments. This does clarification most certainly not imply, as some people have foolishly argued, that "the Orthodox Church" is a "sister Church" of "the Catholic Church". Nor does it mean that "the Moskow Patriarchate" is "a sister Church" of the "Latin Church".
By "particular Church", what is meant is a Church constituted organically with a Bishop, his presbyterate, his diaconate, and all the holy People of God. That is a true Church by divine right, and, incidentally, this is why from time to time it becomes necessary to remind everybody that Catholic ecclesiology has no place for "national Churches"; and views with justified suspicion any movements towards giving Episcopal Conferences anything other than minmal and practical functions. As Cardinal Mueller once wisely said, we must never think of the Chairpersons of Episcopal Conferences as any sort of vice-popes. Nor, as he made clear, must Conferences and their bureaucracies come between the Diocesan Bishop and the Bishop of Rome, each of whom (unlike the Conferences) is iure divino.
What this definition of "Particular Church" means is, for example, that the Diocese of S Petersburg, and the diocese of Brentwood, are true sister Churches; it being understood that the Diocese of S Petersburg is a true particular Church but "wounded" by its separation from the See of S Peter; and the Diocese of Brentwood is wounded by the schism which hinders the Catholic Chuch from realising and manifesting the complete fulfillment of her universality in history.
This, I think, is why we need have no hesitation in recognising those Coptic peasants who, murmuring the Name of their Redeemer, had their throats cut on that Mediterranean beach as "our" martyrs.