Homomorphic encryption would allow for "true security" where the party doing the computation doesn't ever have the encryption keys necessary to see what data they're operating on. This is something more akin to a TPM. The key that can read all of the data is in the possession of the party doing the computation, but it's stored in the CPU and the CPU will not give that key to anyone. Theoretically the key could be read off of the CPU but in practice this would require either a flaw, sidechannel, or a lot of time with an electron microscope.

For practical purposes, I believe that all implementations of secure cloud computing are going to be like this where the key is just secured physically. It's possible with homomorphic encryption to have someone securely do computations on data that they can't see all in software, but I just don't see any major breakthroughs happening that would make this fast enough to be practical.