Notify custom property changes

Question

Hi,
    I am writing small windows application in WPF. I am using UserControl in WPF form. I have custom public property in UserControl called "bDirty" and same property in the WPF form (public) too.
    How can I detect changes in USerControl.bDirty property in Window1.bDirty?

I am using VS 2008, C#. Please help!!

Sample code is appriciated.
Thank you
Guy