What would cause not every computer getting a website's new homepage? See detail?

EDIT: My original answer was about Domain Propagation, I did not read the question carefully and now I think It sounds like a cache issue.

Computers store web pages, so if you ask for the same page repeatedly they can use a local copy instead of going to the original source.

There are many levels of caches. The cache might be on the viewer’s machine. Or the servers at the viewer’s location. Or at the Internet Service Provideer ( ISP ) of the viewer’s site.

If that is the problem, it should disappear soon.

@jaytkay I appreciate that. I hope someone else will benefit from your answer. It is way over my head for me.

The first thing to try is to simply click the refresh button on the title bar when the page is up.

on a pc:
If refreshing the page does not work, go to the control panel of your computer and then to internet options, Under internet properties, go to the general tab. Under that tab delete the temporary files in the browsing history.

If you are too cautious to do this, get help and take notes. You should do this once a month or so. I do it much more often as it speeds up my computer browsing and allows new pages to upload.

It depends on how exactly they changed the homepage. Did they just recode the HTML? If so, it’s most likely a caching issue on the users’ computers. Did they actually change the DNS routing? If so, DNS resolution propagation takes time, and most computers will generally catch up within 24 hours. Do they use a round-robin style of hosting, so that multiple hosts serve the same page? If so, they may have only switched over some of their hosts to the new page, as a form of a beta test.

@jaytkay, I don’t know which is the cause, but what could an owner of a website do to prevent it?
@MaryW Sometimes it I not possible to change anything in “internet option”.
@MrItty that is over my head. What is beta test? what is it is for?

what could an owner of a website do to prevent [caching]

The owner can make changes to the settings on their web server.
Instructions here:
http://www.mnot.net/cache_docs/#IMP-SERVER

@flo a Beta Test is when a company wants to try out a new feature, but it’s not ready for their entire user base yet. So they release the change to a small percentage of their users.

Basically, unless this is really a caching issue on the end users’ computers, there’s absolutely nothing the end users can do about it.

@jaytkay
@MrItty
Thank you. If there is nothing to notify the users who don’t see the new homepage, then that is a problem. I that causes people to give people the wrong instructions, for example. That is just the least serious of problems.