My family roots are in Galloway and have always been told that the Scottish Dougans were originally from there and nowhere else! There is a Loch Dougan in Kirkudbright and a place called Douganhill.
There was also a 15th century bishop of Galloway named Dougan(or Adougan to be exact).
I would be interested to know if anyone disputes this origin of the Dougan clan.