[Discuss] Can a Duke remove a region lord from his Duchy?

[Samuel Knowlton]

> Once someone has been given a lordship they are entitled to it in
> exactly the same way as if they'd inherited it from their father and
> it had been in their family for centuries. To remove someone's title
> is an extreme act and not one a duke can take it upon themselves to
> do, even to a vassal.

Then what mechanism does a Duke have to resolve a grievance with a landed 
vassal? He has oaths with good marks and bad ones for his regular knights; a 
landed noble has an obligation just as a knight does, and if he isn't 
fulfilling it, what is to be done?