Nested sortables

Do you have some quick idea how could be nested sortable achieved?

Use case:
Lets have a grid table with rows and columns. Cells inside rows are sortable and also rows inside table are sortable.

Problem:
Dropping cell in row fires also drop in table.

My possible solution:
1. checking if dropped item is from child list
or
2. isolated scopes for sortables
or
3. something else..

:)
