Limpar cache de verniz com capistrano

Um exemplo simples, como limpar o cache de verniz com capistrano 3.

namespace :varnish do
set :varnish_auth, "/etc/varnish/secret"
set :varnish_address, "127.0.0.1:6082"
set :varnishadm, "/usr/bin/varnishadm"

desc
'Flush entire cache'
task
:flush_all do
on roles
(:web) do
execute
"#{fetch(:varnishadm)} -T #{fetch(:varnish_address)} -S #{fetch(:varnish_auth)} ban "req.url ~ ^/""""
end
end

desc
'Flush assets cache'
task
:flush_assets do
on roles
(:web) do
execute
""#{fetch(:varnishadm)} -T #{fetch(:varnish_address)} -S #{fetch(:varnish_auth)} ban ""req.url ~ ^/assets/""""
end
end
end