The process is basically one of trust. There is NO command for cross-server trading, so basically you would have to know or trust someone on the server you are trading from.
For example; Bogs (your character) has a holocron on Gorath that he wants to get to his character on Bloodfin. Bogs would have to /shout "looking to trade holocron on this (Gorath) server for one on Bloodfin server". When and if someone who has a character with the opposite problem (i.e. they need to get their holocron from Bloodfin to Gorath) hears you, and that is a big "if", then the deal can be made. However, someone will have to trust the other with their holocron first - 'til they can log onto the other server and meet up at a predesignated area. Then the deal can be completed.
One thing to bear in mind is that the holocron most likely does your alt or secondary character little good, unless you intend to try to open FS for both of your toons. With that in mind - if you were to get taken by someone you really haven't lost much, and technically, that sort of trading is not supposed to happen anyway.