One correction: Purgatory is an invention of the Western Church.
The Eastern Orthodox Church has never taught or believed in Purgatory. Nor did the Eastern Church Fathers.
The Eastern Orthodox nor Greek Catholics who are under for that matter use the term purgatory, but their beliefs amount to the same thing.
It comes down to a matter of terminology. I might add that Rome doesn’t require Eastern Catholics to believe in superogatory works, etc.
Besides the whole notion of imputed righteousness is a 16th century innovation.
The church fathers on the state of purification after death (purgatory). http://www.cin.org/users/jgallegos/purg.htm