dstiles - 8:40 pm on Aug 14, 2011 (gmt 0)
1script - were it my SE I would only cache for a short-ish time, possibly for the length of a full scan. If, on the next scan day, they retried the domain name lookup and your working DNS server was unreachable for some reason, they would probably ignore you for a day or so?
The same may not be true of a human, who may well hit the Try Again button on the browser and possibly get lucky, depending on the reason for the response failure and the actual delay involved.
You could always add a third/fourth DNS server to your domain regardless of your second one not working. This is fairly easy to do (there are third party DNS servers available for free or small fee) if you have access to the domain's setup. If you have to rely on your hosting company for this then ask them to do it.