Currently there is no way for the Client API to navigate to a different part of the sitemap.
There is an undocumented way of doing this:
Xrm.Navigation.navigateTo({ pageType:"entitylist", entityName:"contact", viewId:"xxxxx", // Optional if you want a specific view viewType:"1039" // Optional if you want a specific view }
Please can we have this supported because using openUrl creates a very jarring UX for the user because a new window opens and the client browser back history is not maintained.