List of common sources and destinations

List of common sources and destinations

I have a class for representing a source file and a destination of where
it will be copied:
public class SourceDestination
{
public string Source { get; set; }
public string Destination { get; set; }
}
I created a list of SourceDestination and I'm attempting to find sub-lists
from this list where multiple source files go to the same destination and
multiple destinations receive the same source files.
For example, if file A and B go to destination C, D and E and file F and G
go to destination C and D, then A, B, F and G share two of the same
destinations, C and D.
Since the SourceDestination class is a source and destination pairing, how
would I achieve this sort of set operation in Linq?