Let me be a little more clear, the Admins of your account’s particular instance should be the only ones that have access to your votes.
Now the question remains about when your account posts/comments into a different instance, who should have access to those votes? Perhaps your instance has a way of obfuscating the votes of any user coming from your instance, or else only the admins of the community that you’re posting into will have access to your votes?
The problem really comes down to how we avoid the problem with duplicating votes. Currently this is easy as each vote is public so every instance can verify the correct vote count. But implementing either of the solutions above will need a way to verify the correct number of votes.
To top it off you would also need a way to detect if a malicious instance had come along and started lying about how many votes had been cast.
One thing we can look at under the hood would be how cryptocurrency works as they have solved both the problem of duplicate values as well as the ability to trust those values being sent. All of the code is free and open source so we can pick out the parts that we need and reuse it. (And no, I’m not telling people to go out and buy crypto).
Z Cash would be a particularly good one to look at as it ensures a “zero knowledge” (or “zero trust”) method of sending the values across “nodes” (or in our case “instances”). Using this, who is voting on what would be hidden, but we could ensure that the values are correct.
Additionally you could probably throw out the second hashing algorithm altogether and just keep the Blake2b hashing algorithm as this one is far more efficient and quick to compute (and that second algorithm was mostly thrown in to prevent people with specialized hardware from being able to come in and beat anyone else running on just a GPU/CPU). github.com/zcash/zcash
However, using this particular method would make it so that not even the instance admins would be able to view the details of anyone’s votes (which may be a good thing after all if we decide that any random instance admin is not to be trusted).