There are no certain contemporary notices of Domhnall, and Domhnall's existence is not explicitly attested in any reliable contemporary source datable to any particular year. https://en.wikipedia.org/wiki/Domhnall_mac_Raghnaill
It follows that these parents: Ragnall mac Somhairle, Lord of the Isles and Fionnghuala of Moray, Lady of the Isles are definitely not proveable as his.
Jason Scott Wills curates. I've removed his parents, but left him because it seems fair enough to presume he did exist from his descent line's name.