Terminating output to Apache before terminating script

Hi, I have a form processing page that takes a substantial amount of time (content indexing on large files). I want to send a "refresh" message to the client as soon as the form has been validated and the data updated, so that the user doesn't have to wait while the indexing occurs in the background. I've tried using a header('Location: ') command to do this, but it doesn't seem to take effect until the script finishes processing, even if I follow it with a flush(). Is there any way to tell Apache that the current page is finished and to output the page? How does Apache detect the end of a PHP page? Thanks in advance, Chris.