Most DNS clients cache the results of name resolution requests. This speeds up name resolution if multiple lookups are done to the same address, such as is common when browsing the web.
Sometimes a bad DNS entry will be cached and you will need to either flush the DNS cache to get rid of it, or wait up to 24 hours for it to be dropped from the cache automatically.
In Microsoft Windows, you can use the command ipconfig /flushdns to flush the DNS resolver cache:
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