Due to several Ethereum blockchain resets by developers, it is important to note we now have at least 2 forks of chains.
One has about ~4000 blocks, the other 10,000+ blocks.
On my PC and on http://etherchain.org/
I see the longer chain.
Solution for developers:
But if the dev team wants to flush and really reset the chain, here is the procedure:
1. announce it in advance (transparency is important!)
2. release team (core developers) must generate a new genesis block
3. hard code the new genesis block hash into a new client, such as new BETA/POC or an actual release.
(+you can have an optional-command line to enter a different genesis block hash, just in case you wanna work on a forked chain to test things)
Solution for end-users:
1. Install same version of client (such as POC3, C++ version, Alethzero)
2. Make peer connection to each other.
This will replace short chains with the longest one.
This way, the older (longer) chain will no longer over-ride the short chain.