Design pattern that pulls data instead of pushing?

I am learning about the observer pattern, which leads me to question is there a pattern that does the opposite.  Where I can pull changes from a group of observable objects.

Say I have a Sudoku Puzzle, and when I enter a number, I want to confirm that no other box in the same row, column, or square has the same number. 

Is there a pattern where I can configure a list of observable boxes and pull their current value?