mongodb $geowithin for multiple collections

Question

I have a collection with geojson points. I have another collection with geojson multipolygons. How can I run $geowithin against all the boundaries in another collection?. Since the data is very large, loading all the boundaries in memory is very time consuming and memory consuming ( sometimes failing ) process. what can be a good approach here? I have not seen any example where boundary ( multipolygon ) field is dynamic ( comming from all rows of db ) in case of $geowithin