How to multiply a "fat and short" matrix with a "tall and thin" matrix using MapReduce?

Assume that $A_{m \times n}$ and $B_{n \times k}$ are to be multiplied to get $C_{m \times k}$. Now if $n$ is too large for a single row $A_{j}$ of $A$ to fit in RAM (and similarly for columns of B) on a single compute node how do we perform the multiplication?