Howto keep a redirect out of cache

Hi list,

I sync wwwoffle at university and I have to authenticate myself first by 
visiting any page in a webbrowser. My Request will be redirected to a login 
page at https://welcome.uni-ulm.de/....
Sometimes it happens that this redirect is fetch insteed of the page I wanted. 
If that's the case I don't know how to get the real one because I'm stuck to 
the welcome page. Even if I log in I will return to it.
I tried to block that subdomain completly but it seems like it did have any 
effect.

I put *://welcome.uni-ulm.de in the Don't Cache Section but it didn't do 
anything.

My questions are,

how do I ignore this special redirect?
how do I delete these wrongly cached pages from the cache without deleting it 
all?
Is there a way to identify a redirect? maybe even to a certain page?

Thanks for your help

cheers
Jon