The easiest way to achieve that is erasing the geoserver cache manually. You can find the cache location at the file geoserver-directory/WEB-INF/web.xml, there is a variable called GEOSERVER_DATA_DIR, if its not present you can add it and specify the location of the cache directory (mine is /geosrverdata):
Then restart tomcat.
Inside of this directory you will find this:
global.xml gwc security styles wcs.xml wfs.xml wms.xml workspaces
inside of gwc you will find a directory for each layer, erase the content of each directory but don't delete the directory itself.
You could automate this work with a cron job, and you could erase the cache every two days or every month or even every 15 minutes.
But remeber that the clients(google maps, open layers, etc) could still using old data, so also make sure to erase the cache at the clients.