The Normans captured Dublin late in 1170, but its Norse ruler Asgall Mac Turcaill escaped to seek help from the Norse of the Isle of Man, and the Scottish Isles. Asgall returned with a fleet in 1171.
Domnall Mac Gilla Mo-Cholmoc negotiated with Milo de Cogan, the head of the Norman garrison in Dublin, and as a consequence was permitted to sit out the final battle for Dublin between the Normans and the returning Norse. This was on the understanding that Domnall and his followers would join the winning side in the slaughter of their opponents.
Smal, Chris (1993) Ancient Rathdown and St. Crispin’s Cell, A uniquely historic landscape. Friends of Historic Rathdown, Greystones.