nsPIAccessibleDocument Interface

 Find the accessible object in the accessibility cache that 
 corresponds to aStartNode or the first ancestor of aStartNode 
 that has an accessible object associated with it.
 Clear that accessible object's parent's cache of accessible children and
 and remove the accessible object and any decendents from the accessible cache.
 New accessible objects will be created and cached again on demand.
 @param aChangeContent     The child that is changing
 @param aEvent             The event from nsIAccessibleEvent that caused the change:
                           Must be one of: EVENT_REORDER (change),
                                           EVENT_SHOW (make visible or create) or 
                                           EVENT_HIDE (destroy or hide)

void invalidateCacheSubtree(in nsIContent aChangeContent, in PRUint32 aChangeEvent)