Can a CloudWatch Event in one region trigger a Lambda in another region of AWS?

An alternative is to have CloudWatch trigger SNS. As per the attached screenshot, SNS topic subscription will allow full ARN declaration, and the dropdown even showed a us-east-1 lambda when I was in US West (Oregon) region.

SNS Screenshot

From the dashboard, it is not possible to trigger cross region Lambda. When you create a CloudWatch event rule, select a Target to invoke, under Lambda function only the lambdas in the current region are shown.