class method static variable same across isntances?

The output of the following program for me is:
Same
0 1 2

Which is what I want. I just want to confirm this is well defined behavior,
that a static local variable to a class function/method is the same instance
across classes.

#include <iostream>
#include <vector>

class Foo
{
public:
    std::vector<int>& Data( )
    {
        static std::vector<int> EmptyData;

        return EmptyData;
    }
    int Bar()
    {
        static int Val = 0;
        return Val++;
    }

};

int main()
{
    Foo Bar1;
    Foo Bar2;
    std::vector<int>& D1 = Bar1.Data( );
    std::vector<int>& D2 = Bar2.Data( );

    if ( &D1 == &D2 )
        std::cout << "Same\n";
    else
        std::cout << "Different\n";

    std::cout << Bar1.Bar() << " ";
    std::cout << Bar2.Bar() << " ";
    std::cout << Bar1.Bar();
    return 0;
}

My actual usage will be to return an empty set in a tree like class if the
part is not found, but within that class I want to check to see if it was
found or not. I can see if it was found or not by comparing the pointers of
the returned reference to the local static.