When I run any query on data.stackexchange.com, it shows old data. In says xx rows returned in xx ms (cached).
The cached data is old one. How to reset/remove this caching?
The data is now updated weekly, on Sunday, at approximately 5 a.m UTC.
When this happens, all of the query result caches are cleared, so you very rarely have to worry that you're getting incorrect results because of caching* as opposed to the data being slightly aged.
*There's a very specific edge case where this isn't true, but no one's come up with a good reason to be concerned about it so far, so you shouldn't be either.