You can't revert directly to with another repository but you can revert a file to its state as of the last fetch or pull from that repository. This is supported by the "Replace With..." operation, with the remote-reference as the target. This is usually something like 'origin/master' under "Remote Tracking". Replace With can also be used to revert to the last locally committed version, or the last staged but not yet committed change, or some other local branch.
Note that this is a completely local operation in all cases. In particular it will not fetch any new changes from a remote repository. That's a separate operation.
As R Shapiro said you can use "Replace With" in eg. package explorer context menu.
You can also use "Overwrite" from file context menu in Synchronize view in "Workspace" presentation model. The "Overwrite" in Synchronize view is equivalent to "Replace With" -> "HEAD revision" from package explorer file context menu and it will restore version latest version of given file in this branch. If you would like to restore version from another branch you need to use "Replace With" -> "Branch, Tag, or Reference..." and then select source branch.
The nightly build has an 'Overwrite' option in the Synchronize view. I don't know for sure what the semantics are here, in particular where it will overwrite from the HEAD, the Index, or the last commit fetched from whichever remote you're synchronizing against. One of the egit authors can no doubt answer that question.
Either way, I think you'll find it more straightforward to perform operations like this from an Explorer view using 'Replace With'. It's a bit roundabout to go through the work of synchronizing if you already know exactly what you want to do. Certainly 'Replace With' is much more explicit about what it will be doing.
In general I've noticed a tendency for Eclipse users to go through synchronization for no particular reason. This is true with subversive/subclipse and cvs, as well as egit. Unless you want to do detailed comparisons of multiple files, there's no reason in any Team provider to pay the price of synchronization.