Donnchadh macGilla Pátraic macDonnchada, a descendant the infamous king
Cearbhall macDúngaile, became powerful enough to claim the kingship of the province of Leinster (a "greater part of" southeast
Ireland) for a short time during 1030's. Shortly after this point, about 1041, we find a notice in the Annals of the Four Masters that Muircheartach mac Gilla Pátraic, a brother of the aforementioned
Donnchadh, and a lord of half Osraighe, was slain by the Ui Caelluidhe (the O'Kealys of Magh Lacha). In Upper Ossory, in what is now part of County Laois, the Ui Caollaidhe (the O'Kealys) were able to exert an independent rule over both their own territory and that of the Ua hUrachan (the O'Horahans of Uí Foircheallain) and the Ua Dubhslaine (O'Delany's of Coill Uachtarach).
Finn O'Caellaide is mentioned as a lord of Ossory on his death notice in 1098, and he is cited as marrying a grand-daughter of Gilla Pátraic macDonnchada (d. 996). After the death of Giolla Pháttraicc Ruadh, a king of Ossory, in 1103, it appears that a junior branch of the Mac Giolla Phádraigs were able to lay claim to the southern-most part of Osraige, aka Deascairt Osraighe (under Cerball macDomnaill), while the main branch appear to have maintained their hold in the large middle portion of the kingdom (possibly the northern two-thirds of modern County Kilkenny).
http://www.rootsweb.com/~irlkik/history/ossory.htm