Just unplug your router and plug it back in. There is often a reset button but if you push that, you'll have to re-configure your router with the appropriate password, etc.
Simply unplugging it will clear the cache but not reset your settings.
Then, there is backbone. It's really fascinating how the world wide web actually works. If you never read about what the www actually is, you might be surprised. There are actually a handful of people who support us all. They are called NSP's (Network Service Providers) Cerfnet, UUnet and a handful of others actually support the entire world wide web. They all share data packets back and forth and they route our data for us to the point where it is supposed to go. They are the ones who rent space to your ISP (Internet Service Provider). Think of it as wholesale and retail. UUNet and CerfNet are the wholesalers. Time-Warner, AT&T, etc are ISP's and they are the retailer (selling to us).
And, on rare occasion, one or more of those NSP's may be having problems. And, when they do, all the sites on the other backbones will work great for you but the sites that are on that backbone will be slow. And, while I connect with MP via one backbone, you may connect via another.So, that's why I may not have a problem and you do.
So, when you have problems with one web site and not another, it is [sometimes] a backbone problem. And, there's not much you can do about that. It's usually cleared up within hours, not days.