How do I check if a file exists using its URL without downloading it?

I need to write code which will determine if a file exists by checking its URL.

Currently I implement this:

error_code = 400;
response = Net::HTTP.get_response(URI(url));
return response.code.to_i < error_code;

But, it's not working right because each time it downloads the file, which is really slow if I have big files or a lot of them.

How do I determine if a file exists on the remote side without downloading it?