I have an Apache server running owncloud on 10.0.0.120:80 and an Apache server for reverse proxy running on 10.0.0.110
/etc/apache2/sites-available/000-default.conf
<VirtualHost *:80>
ProxyPass /owncloud/ http://10.0.0.120:80/
ProxyPassReverse /owncloud/ http://10.0.0.120:80/
</VirtualHost>
In a browser
10.0.0.110 and 10.0.0.110/owncloud currently redirect to 10.0.0.110/index.php
10.0.0.110 should resolve to redirect to /var/www/html
10.0.0.110/owncloud should redirect to 10.0.0.120:80/index.php