How to propagate property change notifications of objects within collections

Lets say I have classes like this

public class R
{
    protected string name;
    protected List<S> listOfObjectS;
}

public class S
{
    private string name, ID;
    private A objectA;
}

public class A
{
    private string name;
    private int count;
}

If a user has two views open, one displaying instances of R and another allowing users to modify an instance of A, I need the view of R to change when the user changes any instance of A.

If the user changes a property of an instance of A, what is the best way to propagate that change (through instances of S) so that all instances of R display the new state of A?