Fast hashing of 2-dimensional array

I'm building a Reversi player using the standard alpha beta pruning search algorithm. I'm trying to add a translation table to store previously calculated nodes in the search tree. So I need to hash a 2 dimensional array representing the game board (the state) and store a value for that.

I can't come up with anything better than a double for loop iterating over my arrays and adding all values together multiplying them with the offsets to get unique hash values.

@Override
public int hashCode() {
    if (dirtyHash) {
        int hash = 0;
        for (int i = 0; i < Board.SIZEX; i++)
            for (int j = 0; j < Board.SIZEY; j++)
                hash += board[i][j] * (i + Board.SIZEY * j);

        hashValue = hash;
        dirtyHash = false;
    }

    return hashValue;
}

I suspect there must be a much smarter way to do this? Anyone got any ideas?