Ingibjorg died probably sometime before 1069, by which time she had given birth to two sons, Duncan and Donald. Never one to squander an opportunity, Malcolm had by 1070 insisted on marrying Margaret, the sister of Edgar the Artheling ('prince'), who had fled to Scotland after the Norman forces of William had taken control of northern England. The marriage would produce two daughters and six sons, three of whom would rule successively as kings of Scots. It would also result in a fierce family squabble over the succession after 1093. In the shorter term, it gave a fresh edge to Malcolm's territorial ambitions, both in Cumbria and Northumbria - whether as ally of Edgar or simply as a warrior king intent on uniting his diverse peoples in aggression.

In 1070 he launched his second invasion, via Cumberland, across Stainmore and into Teesdale, carefully circling rather than pushing directly into Northumbria. There were two unusual features of this expedition and both may indicate that Malcolm in 1061 had already secured a hold on Cumbria - the most mysterious of all areas in early medieval Scottish history. It was the only Scottish invasion in the eleventh or twelfth centuries to originate in the west and his army was mainly composed of men of Galloway. Whatever its intentions, the invasion of 1070 ended in confusion before the walls of Durham with much of the booty lost. Retaliation came in 1072 when William entered Lothian and crossed the Forth into Fife at the head of a large army, with a fleet in support. This campaign - the first full-scale invasion of Scotland by a well-organised English army - also ended inconsequentially. At Abernethy on the River Tay, some 250 miles away from his base at York and frustrated by Malcolm's Fabian tactics, William settled for an assurance from Malcolm who 'made peace…and gave hostages and was his man'. For William (and for subsequent English chroniclers over the next six centuries) the act may have been a formal act of homage of a vassal, but for Malcolm it was an empty gesture which, despite the fact that one of the hostages was his eldest son Duncan, could be discarded when opportunity next presented itself- which it did in 1079, with Norman authority in the north in a state of collapse. Again, in 1080, a Scots expedition provoked an English counter-strike, this time led by William's son Robert Curthose, which failed to lure Malcolm into battle. At Falkirk the terms leached at Abernethy were renewed, more hostages were arranged and a border as far south as Stainmore and the Tyne was agreed - a frontier also confirmed by the rapid building by Robert on his march south of a fortress on the Tyne, the 'New Castle', some eighty miles south of the Tweed. It was the high-water mark of Malcolm's ambitions to re-establish the old Dark Age kingdom stretching from the Forth, if not to the Humber, at least to the Tyne.