Change the definition of Override in /etc/httpd/conf/httpd.conf

# AllowOverride controls what directives may be placed in .htaccess files.
# It can be "All", "None", or any combination of the keywords:
#   Options FileInfo AuthConfig Limit
    AllowOverride All

Then create the following .htaccess into the DocumentRoot.

Options +FollowSymLinks
RewriteEngine On
RewriteCond %{HTTP_HOST} ^ [NC]
RewriteRule ^{REQUEST_URI} [L,R=301]

so. it got change and redirected automatically .. to new domain.
if user happened to access it via the old domain.

This is important when some session data is stored within the domain name.