http://services.arcgisonline.com/ArcGIS/rest/services/World_Street_Map/MapServer
http://services.arcgisonline.com/ArcGIS/services/World_Street_Map/MapServer?wsdl
The REST API caches content pertaining to catalogs, services, maps, models, etc. Caching such content allows significant performance impovements while working with the REST API. However, you need to clear this cache when you add services, remove services, update services, or update to a new version of the REST API.