If you only want to save one data source, the best method is probably to specificaly save that datasource. To do that, change the button type from Submit to Button. Then use SSJS to call the save method for your DominoDocument datasource. By default the first datasource will be document1, so it would be document1.save();

 

If you then want to go to a specific XPage after this function, you can add a simple action afterwards. If you always want to go to the same XPage after successful processing, you've got a property on the main pretty panel for the XPage itself to define the next XPage after success or failure (by default the same page). If that doesn't cover what you need, you can always use Navigation Rules. It's explained in Mastering XPages, I've blogged about it http://hermes.intec.co.uk/Intec/Blog.nsf/dx/10122009184850HERQ3K.htm, and so did Jeremy Hodge on The XPages Blog http://xpagesblog.com/xpages-blog/2010/8/9/using-navigation-rules-in-your-xpages-application.html