John Hadzor's Castle.

Maghernacloy Castle today. From:
The Buildings of Ireland Web.

In around 1618, the 3rd Earl of Essex granted John Hadsor of Keppok lands around Moymuck, lands that just so happened to have belonged previously to the MacMahon clan. Maghernacloy Castle was built on these lands, very possibly by John himself. It would seem that the Hadzors and Macmahons were still in some kind of alliance, in so much as they agreed that whatever their own differences might have been, they were nothing as compared to the breach between themselves and their common enemy, the English government.   

Maghernacloy castle as it turned out was just one of the Hadsor possessions that would pass into Cromwellian ownership. According to article on the Duchas website, it was the Macmahons who were in possession when the final assault came. They refused to surrender until the upper story had been destroyed by cannon fire. The article continues to report that:

Before the chieftain surrendered he packed all his wealth of money and valuables in a chest and had it drawn by two bulls to a well known as the Lughbawn and thrown in. It is told that in later years a few people collected with grappling irons and chains and tried to recover the hidden treasure. When they got the chest up to the water level a little man riding a white horse came galloping past attracting the men's attention. They let the chest slip back into the well, and it has never been recovered since. People in the locality still tell of steps that ascended the stone stairway at night and a light that moved along the roof,and other strange disturbances which continued until the intruder was confined to a room and the door built up.

http://www.duchas.ie/en/cbes/4723811/4715543

In such ways did Irish lands transfer themselves from the native Irish clans to the English aristocracy, back to the Anglo-Norman families and through the Irish back to the English colonists.