according to J J Kneene - Ballagarraghyn, Treen []. (in German)
1526 Man. Roll Balydorgan
1643 ,, ,, Balladoraughan
1703 ,, ,, Balla Gharrahen
‘Dorgan or O'Dorgan's farm' (Ir. O'Dorcháin), Lost surname. The metamorphosis of Dorgan or Doraughan into Garraghyn suggests that mac had replaced o before the name disappeared.

maybe consult Broderick (in Museum) as I doubt you can afford a copy (I certainly can't)