Clears the source's cache of loaded pages. This occurs when an outside change to the world invalidates
created page instances. Introduced to handle the case where a page has a DynamicTemplate, but the
underlying Resource is noticed to have changed.
Returns all currently loaded pages. This will include any previously loaded pages not yet reclaimed by the
garbage collector, and may include the same page loaded for different ComponentResourceSelectors. This is needed
for reporting purposes only.