I am running Apache witha redirect rule like this:
RewriteCond %{HTTP_HOST} ^1st-domain\\.com RewriteRule ^(.*)$ http://2nd-domain.com$1 [R=permanent,L]
This should work:
RewriteCond %{HTTP_HOST} ^1st-domain\.com RewriteRule ^(.*)$ http://2nd-domain.com$1 [R=permanent,L] RedirectMatch ^/$ http://3rd-domain.com