Another good thing about removing double content is to remove or add www prefix to your domain.

Remove WWW from domain

# This will remove www from your domain
RewriteCond %{HTTP_HOST} ^www.mediabox.lv$ [NC]
RewriteRule ^(.*)$ http://mediabox.lv/$1 [R=301,L]

This is what I now use for all my domains – domain without www prefix.

Add WWW to domain

This probably is best for old domains like mine www.rolandinsh.lv

# This will remove www from your domain
RewriteCond %{HTTP_HOST} ^mediabox.lv$ [NC]
RewriteRule ^(.*)$ http://www.mediabox.lv/$1 [R=301,L]