How to find which objects are selected on a given layer?

`bpy.context.scene.selected_objects` shows objects only on visible layer(s). After switching to another layer, the list of selected objects is gone.

```
>>> bpy.context.scene.layers[0] = False
>>> bpy.context.scene.layers[10] = True
>>> bpy.context.scene.object
bpy.data.objects['Cube']

>>> bpy.context.scene.selected_objects
[]

>>> bpy.context.scene.layers[0] = True
>>> bpy.context.scene.selected_objects
[bpy.data.objects['Cube']]

```