As far as I know there are two ways to reload a linked library (so the linked objects update to the state they are in the source file) in Blender 2.8:

1. Close and reopen the file with the linked library.
2. Reload button inside the Outliner > Blender File > RMB (over the linked linked .blend file) > Reload.

The reload button seems to call an Outliner operation: bpy.ops.outliner.lib_operation(type='RELOAD'). But I think is not a good idea to call bpy.ops.outliner from a script (neither I can find a way to do it). I think must exist some other call over bpy.data to to the same thing (and safer than call a operator), but I cannot find it.

Is there a way to reload the linked library from a script? If the only way is calling the above mentioned "outliner operation", how can I call it from a script?

I'd like to iterate over all linked libraries and update them.

Thank you.

bpy.data.libraries[YOUR BLENDER FILE NAME HERE].reload()