Serious defeats in Ireland and Scotland in the time of Domnall Brecc ( d. 642 ) ended Dál Riata 's `` golden age '' , and the kingdom became a client of Northumbria , then subject to the Picts .
Defeats in Ireland and Scotland during the reign of Domnall Brecc ( d. 642 ) ended Dál Riata 's dominance . The kingdom came under the control of Northumbria , then subject to the Picts .