You have to copy it to the zone in which you want to start the new instance.
From Amazon EC2 documentation:
How do I launch an AMI in another Region?
Simply copy your AMI from its current
bucket to a bucket located in the
Region where you want to launch the
AMI and register the AMI. For example,
to launch a US-based AMI in the EU
Region, you have to copy the AMI to an
Amazon S3 bucket that was created with
an EU location constraint. After the
AMI is copied, you must register the
AMI and use the obtained AMI ID for
launches in the new Region.
Also, make sure to give read access to
the bucket, image manifest, and image
parts to ec2-bundled-images@amazon.com
for Windows AMIs, and
za-team@amazon.com for Linux AMIs.
What tools are available to help
*migrate my AMIs to a new Region?*
The API Tools contain a new command
called ec2-migrate-image. It is
designed to help migrate AMIs to a new
Region. Run ec2-migrate-image --help
for more details.
