As per the documentation quoted by kcott, shared variables are valid only if all parts (other than “simple values”, i.e., non-reference scalars) are explicitly shared. So, to declare and initialise the hash, you will need syntax something like this:

my %host_info :shared =
(
    1 => &share
    (
        {
            hostname  => 'somehost@somewhere.com',
            host_info => &share
            (
                {
                    info  => 'valueA',
                    info2 => 'valueB',
                    info3 => 'valueA',
                }
            ),
        }
    ),
    2 => &share
    (
        {
            hostname  => 'someotherhost@somewhere.com',
            host_info => &share
            (
                {
                    info  => 'valueA',
                    info2 => 'valueB',
                    info3 => 'valueA',
                }
            ),
        }
    ),
);
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See Re^3: How to share complex data structure in threads ? by BrowserUk.

Hope that helps,