Imagine an arbitrary point in space. It is within the gravitational potential of every mass (although billions of ly away) in the entire universe.

Since every mass adds a tiny fraction, what is the total gravitational potential energy in this point?

Edit:

Let point masses be located distance $r_i$ from the point and have masses $m_i$, then the potential is

$$\Phi = - G \sum_{i} \frac{m_i}{r_i}.$$