Retrieve taxonomies from arbitrary site

Background

I need to retrieve terms for a post in an arbitrary site on a multisite network. This is not necessarily the site that the WP instance is running in at that moment. wp_get_object_terms() requires the taxonomy for which to retrieve the terms. So, to retrieve all terms for all taxonomies, it would be necessary to first retrieve the taxonomies. This does not appear to be possible, as the taxonomies that are registered by plugins may not be getting registered on the current (original) site that the instance is running in, because the plugins themselves would not be active on that site.

Question

How can I retrieve all taxonomies for a post in an arbitrary site?

Alternatively, how can I retreive all taxonomy terms for a post in an arbitrary site?