Apache: Control access with .htaccess file to a directory

Question

I am trying to restrict access to a directory in my shared hosting account on GoDaddy. Basically, that means I have no access to the httpd.conf file for their Apache server, so I have to use .htaccess files to control access to everything.

I have two domains on the shared hosting account, which we'll call domainA.com (the main domain), and domainB.com (an additional domain). domainA.com is mapped to / (the root of my shared storage), and domainB.com is mapped to /.domainB. What I want to do is prevent access to http://domainA.com/.domainB and only allow access to that folder if the http request is for http://domainB.com/

Does that make sense? I think GoDaddy is running Apache 1.3. I have tried the following code in an .htaccess file at / :

<Directory .domainB>
   Order deny,allow
   Deny from all
   Allow from domainB.com
</Directory>

But that results in a 500 error when trying to access the page either way. Can someone help point me in the right direction?